The Rotafix is a method of tightening or loosening a
sprocket
A sprocket, sprocket-wheel or chainwheel is a profiled wheel with teeth that mesh with a chain, track or other perforated or indented material. The name 'sprocket' applies generally to any wheel upon which radial projections engage a chain pass ...
on a
track bike or
fixed gear
A fixed-gear bicycle (or fixed-wheel bicycle, commonly known in some places as a fixie) is a bicycle that has a drivetrain with no freewheel mechanism. The freewheel was developed early in the history of bicycle design but the fixed-gear bicy ...
bicycle.
Method
The Rotafix enables the securing of a sprocket ("cog") to a track hub without the use of a
chain whip.
The chain is removed from the
chainring
The crankset (in the US) or chainset (in the UK), is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain or belt, which in turn drives the rear wheel. ...
and rests around the bottom bracket shell and on the sprocket with the rear wheel in the horizontal track ends. The chain is folded over itself such that the bottom half of the chain is trapped between the sprocket and the upper half. The sprocket is then prevented from turning because the chain is wrapped around the bottom bracket. It is essential to take steps to protect the paintwork on the bottom bracket shell from damage by the chain.
The sprocket is then tightened onto the hub by turning the wheel backwards until it is too tight to turn any more. This method can tighten the sprocket to very high torque because of high
mechanical advantage
Mechanical advantage is a measure of the force amplification achieved by using a tool, mechanical device or machine system. The device trades off input forces against movement to obtain a desired amplification in the output force. The model for ...
created by the wheel. Professional mechanics also refer to this method as "frame whipping",{{fact, date=April 2021 as there is no need to utilize a
chain whip.
Removing the sprocket is done by reversing the chain fold so that it is on the bottom and turning the wheel forwards so that the sprocket turns counterclockwise. This is called the Reverse Rotafix.
External links
Securing a Track Sprocket Without Lockring
Gears